Channel plate and manufacturing method thereof

ABSTRACT

To provide a plate of high resolution and large area. The channel plate configured by including a substrate, a first electrode placed on the top face of the substrate, and a second electrode placed on the bottom face of the substrate, wherein the substrate is a porous element having a plurality of pores extending therethrough, and the porous element is formed by a compound including aluminum, and the porous element has an electron multiplier on a wall surface of the pore.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a channel plate used for an imageintensifier, a photoelectron amplifier and so on and a manufacturingmethod thereof.

2. Related Background Art

An electron multiplier using a secondary electron emission phenomenon,such as a photomultiplier, is widely in the actual use. The electronmultiplier has a mechanism having a channel comprised of an interiorwall of a glass pipe or a ceramic pipe, wherein an electron acceleratedby an electric field is collided against the surface of the wall of thechannel to generate a plurality of secondary electrons. Such electronmultipliers are made in micro-size and integrated in a high density soas to form a channel plate of a planar structure (also called amulti-channel plate, micro-channel plate and so on), which is used foran image device such as an image intensifier. In recent years, asrequirements for the image device, not only more higher level ofperformance such as higher density, higher sensitivity, higher-speedoperation and wider dynamic range, but also larger a size design morethan the micro-size and a simple production method in order to provide adevice with larger area and higher resolution. For that purpose, a largechannel plate wherein electron multipliers are integrated in a densityhigher than the micro-size is required.

For higher resolution of channel plate, it is necessary to integrateindividual electron multiplier in a high density. For that purpose, itis desired that channel wall thickness to each channel opening is small.Moreover, a plate having a stable channel wall hardly destructible overlarge area is required for a large-size channel plate that is largerthan the micro-size.

The conventional electron multiplier uses glass such as lead glass andceramics because of the necessity to form a tubular internal wallsurface. The conventional multi-channel plate is formed by extendingbundled glass pipes in a heated and softened state to form a platehaving many pipes, or as shown in Japanese Patent Application Laid-OpenNo. 2000-113851, or, it is formed by coating a wire surface with diamondfilm, adhering the coated wire with an insulating substrate such as aplurality of adhesives, cutting the insulating substrate into plate-likeelements, removing the wire by etching to form electrodes on both sidesof the plate-like element respectively, or as shown in Japanese PatentApplication Laid-Open No. 4-87247, it is formed by forming a pipe on ahigh lead glass substrate by etching and then heat-treating it inreducing gas atmosphere such as hydrogen.

FIG. 5 is a perspective view illustration showing configuration of theconventional channel plate. On a glass insulating substrate 21, aplurality of channels 22 are formed by etching, and a cathode electrode24 and an anode electrode not shown therein are formed.

As for the conventional channel plate formed by using glass, it isnecessary to decrease a diameter of the channel opening such that thediameter is smaller than the channel wall thickness in order to enhancestrength of the glass to be the substrate. Accordingly, it is possibleto make it larger but there is a limit to making it higher-resolution inthe case of using a glass substrate as the substrate.

In addition, while the method of forming pores by cutting glass pipes orwires after bundling them in an adhesive layer and etching them issuitable for rendering a small plate higher-resolution, it is necessaryto enhance adhesive strength against the etching for the purpose toallow the larger area design. Accordingly, the area occupied by theadhesive layer in the pore opening must be large enough. Moreover, inthese methods, a semiconductor layer may be formed by heating thechannel internal wall glass surface at high temperature in reducingatmosphere such as hydrogen. In such cases, a problem of heat strainsdue to high temperature heat treatment arises. Furthermore, as the wireto be a mold of the electron multiplier surface is removed by strongacid etching after forming a coating of diamond and so on, it wasnecessary to form the electron multiplier surface, which is the coating,as a robust coating that is maintained even without the wire.

SUMMARY OF THE INVENTION

The present invention was implemented in order to solve the problem setforth above, and its object is to provide a multi-channel plate that hashigh resolution and is advantageous for larger area, high resolutiondesign and a manufacturing method thereof.

Another object of the present invention is to provide a channel platehaving a structure of an electron multiplier surface capable ofincreasing a secondary electron multiplication factor and themanufacturing method thereof.

To be more specific, the channel plate according to the presentinvention is one having a porous element, and is characterized by theporous element including an aluminum compound.

In addition, the channel plate involved in a second invention of thepresent invention comprises: a substrate; a first electrode placed onthe top face of the substrate; and a second electrode placed on thebottom face of the substrate, wherein the substrate is the porouselement having a plurality of pores extending therethrough, and theporous element is formed with a compound including aluminum, and theporous element has an electron multiplier on a wall surface of the pore.

It is desirable that the above described electron multiplier emitssecondary electrons due to collision of the electrons with the abovedescribed electron multiplier.

It is desirable that the above described electron multiplier has oxidegrains of which secondary electron emission coefficient is larger than1.

It is desirable that the above described porous element has aluminumoxide as its main ingredient.

It is desirable that the above described electron multiplier is formedby coating the wall surface of the pore of the above described porouselement.

In addition, a third invention of the present invention is a channelplate manufacturing method comprising the steps of: anodizing aluminumor the substrate of which main ingredient is aluminum to form the porouselement having a plurality of pores extending through the substrate;forming the electron multipliers on the wall surface of the pores; andforming the electrodes on the top and bottom faces of the porous elementrespectively.

It is desirable that the above described step of forming the electronmultipliers is a step of coating the wall surfaces of the pores of theabove described porous element with a coating layer including a materialof which secondary electron emission coefficient is larger than that ofthe material forming the above described porous element.

It is desirable that the above described coating layer comprises amaterial of which secondary electron emission coefficient is larger than1.

It is desirable that the above described aluminum or the substrate ofwhich main ingredient is aluminum is an aluminum film disposed on theelectrode to be anodized.

It is desirable that the above described coating layer includes oxidegrains.

According to the present invention, it is possible to provide thechannel plate wherein a channel having the electron multiplier surfaceof which electron multiplication factor is improved is formed over largearea. It is possible, by using this channel plate, to acquire a largeimage intensifier of high resolution and large area, which can meet thedemand for larger area design and higher performance in recent years.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic section views showing an embodiment of achannel plate of the present invention;

FIG. 2 is an enlarged section view of a single channel comprising thechannel plate of FIGS. 1A and 1B;

FIG. 3 is a schematic section view showing an embodiment of the channelplate of the present invention;

FIGS. 4A, 4B, 4C and 4D are diagrams showing manufacturing steps of thechannel plate of FIGS. 1A and 1B; and

FIG. 5 is a slanted view of a conventional channel plate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail hereafter.

Channel plates of the present invention and a manufacturing methodthereof will be described with reference to the drawings. Like portionsin the drawings refer to the same reference symbols.

FIGS. 1A and 1B are illustrations showing an embodiment of the channelplate of the present invention, where FIG. 1A is a section view and FIG.1B is a slanted view. As shown in FIGS. 1A and 1B, the channel plate ofthis embodiment is comprised of a channel 2 wherein a substrate 1 and apore 6 provided in the substrate 1 are placed, and an electronmultiplier 3 for emitting a secondary electron due to collision of theelectron is formed on an internal wall surface of the pore 6, and acathode electrode 4 and an anode electrode 5 provided on the top faceand on the bottom face of the substrate 1 respectively for the purposeof applying voltage to the electron multiplier 3. And it ischaracterized by the substrate 1 comprised of a compound includingaluminum.

The compound including aluminum referred to here is primarily a compoundsuch as aluminum oxide, aluminum hydroxide, hydrate and so on generatedfrom aluminum in an aqueous solution. As a matter of course, it may be amixture of a plurality of these compounds. Moreover, in the case where aporous element is primarily composed as the aluminum oxide, the elementis substantially an insulating substrate.

In addition, electron multipliers are placed on the internal wallsurfaces of a plurality of pores, thus forming a so-called electronmultiplier surface in a channel plate. It is desirable that the electronmultiplier surface has oxide grains. This configuration increasesmicroscopic asperities on the face of the electron multiplier surfaceand its surface area becomes larger than an even surface so that asecondary electron multiplication factor can be improved.

Moreover, a method of manufacturing the channel plate of the presentinvention is characterized by forming the wall surface of the channel byanodizing the aluminum.

In addition, it is characterized by having the steps of: anodizing in asolution the substrate of which main ingredient is aluminum to form aplurality of pores; having the pores extend through the substrate;coating the internal surfaces of the pores with high secondary electronemission material; and forming the electrodes on both faces of thesubstrate on which the pores are formed respectively.

Furthermore, it is characterized by the substrate of which mainingredient is aluminum being an aluminum film placed on the electrode tobe anodized.

If an aluminum plate is anodized in the present invention, an anodicoxide alumina layer that is a porous anodic oxide film is formed. Thisporous film is characterized by having a unique geometrical structurewherein extremely minute columnar pores (nanoholes) of which diameter isbetween several nm and several hundreds nm are arranged in parallel withspacing of several tens of nm to several hundreds nm. These columnarpores have a high aspect ratio and also good uniformity of sectionaldiameters.

An insulating substrate 1 is comprised, for instance, of aluminum oxideor a mixture of aluminum hydroxide and so on, and as shown in a slantedview of FIG. 1B, the channel 2 in which an electron multiplier surface 3is formed on the internal surface of the pore 6 extending through thesubstrate is placed, and the insulating substrate 1 is formed to beapproximately several hundreds μm to 1 mm thick, and to have thediameter of 10 cm for instance in order to form a multi-channel plate.

The channel 2 has a diameter of several μm to several hundreds μm or so,and a million pieces or more of it are formed, for instance, in order toform the multi-channel plate for an image intensifier.

Moreover, the pores of the porous element may be formed substantially ina vertical direction from a top electrode 4 to a bottom electrode 5.

In addition, as shown in FIG. 3, the pores may be formed in a slanteddirection to a thickness direction of the substrate so as to increasethe number of the times that the electron collides with the pore wallsurface. Or, it is also possible to render the pore diameter on the topface of the porous element different from that on the bottom face.

FIG. 2 is an enlarged section view of a single channel comprising themulti-channel plate in FIGS. 1A and 1B. The internal wall surface of thepore 6 of each channel 2 is the electron multiplier surface 3, and theinside of the channel 2 is a hole. There are the asperities on the faceof the electron multiplier surface 3, and formation of the asperitiescan dramatically enhance a nucleus occurrence density so as to improvethe secondary electron multiplication factor.

It is easy to form a surface that is uneven with irregular asperities onthe electron multiplier surface 3. For instance, as the pore that is theelectron multiplier surface 3 has a grain 3 a of an oxide or the like onits internal wall surface, it increases microscopic asperities on theface of the electron multiplier surface and the surface area thereofbecomes larger than an even surface so that a secondary electronmultiplication factor can be further improved.

The cathode electrode 4 and the anode electrode 5 are intended to applya potential to the electron multiplier surface 3, and they are form withmetals such as Au/Ti and Al to be approximately 0.1 to 0.5 μm thick.

The electrodes do not have to be formed in the entire area of the topand bottom faces of the porous element but only in part thereof.

The channel plate of the present invention has the channel includingaluminum formed by regularized Al anodic oxidation.

The manufacturing method of the channel plate shown in FIGS. 1A and 1Bwill be described by referring to FIGS. 4A to 4D.

First, as shown in FIG. 4A, a substrate 10 of which main ingredient isAl that is the material of the insulating substrate 1 is soaked in anelectrolyte for anodic oxidation to form the pore 6 as shown in FIG. 4B.

Here, the substrate of which main ingredient is Al is the materialforming the pore by anodic oxidation and having a portion in which themetal Al is constituted with required area and thickness, where a metalAl plate and a board forming electrodes having an Al film piled upthereon and so on can be named. Moreover, other elements may be includedas far as they can be anodized. In addition, a vacuum evaporation methodby resistance heating, a sputtering method, a CVD method and so on maybe used to form the aluminum film. However, a method capable of forminga film with a surface that is even to an extent is desirable.

The electrolyte is liquid for forming the pore while oxidizing the metalAl by applying desired voltage, for which an aqueous solution ofphosphoric acid, oxalic acid, sulfuric acid and so on adjusted to adesired density is used. The spacing, depth and so on of the pores canbe changed by controlling a current density and time. In the case of apore forming method by anodic oxidation using aluminum, homogeneous andregular pore formation is possible by regularly forming desiredasperities to be a starting point of the pore formation on the aluminumsurface in advance. That is, as a concave portion on the aluminumsurface is more easily oxidized, the aluminum dissolves as the oxidationprogresses so that the pores are successively formed.

As a method of forming such regular asperities on the aluminum surface,a method whereby a focusing ion beam is used, a method whereby a stampwith the asperities is pressed on the aluminum surface, a method wherebya convex portion is regularly formed with a resist or something similarand so on can be named. In addition, the pore formation regularized overlarge area is possible by performing two-phase anodic oxidation. To bemore specific, it is a method whereby a porous coating formed by theanodic oxidation is removed once and then the anodic oxidation isperformed again so as to make the porous coating with the pores showingbetter verticality, linearity and independence. This method is using thefact that a concave on the surface of the Al plate created when removingthe anodic oxidation coating formed by the first anodic oxidationbecomes the starting point for the pore formation of the second anodicoxidation.

To be more specific, if an oxidation zone is etched after performing theanodic oxidation once and the anodic oxidation is performed again, theremainder of the first oxidation zone forms the asperities on thealuminum surface so that the pores are regularly formed.

Thus, an extremely thin oxidation zone is left on a pore bottom 11 thatis regularly formed. This zone is removed to have the pore extendthrough the substrate and form the channel 2 as shown in FIG. 4C. As fora method of removing the pore bottom 11, chemical etching, a method ofphysically shaving it and so on can be named. The pore diameter can beextended thereafter by performing a pore-widening process as required.

The inside of the pore 6 thus formed by the aluminum anodic oxidationforms an uneven surface with irregular and minute asperities. It ispossible thereafter to have even more minute asperities formed insidethe pore by coating the inside of the pore with grains. Thus, formationof the minute asperities inside the pore that is the electron multipliersurface 3 of the channel 2 increases the number of times of collisionand scattering of the electrons incident inside the channel, and a formcan be acquired, wherein the surface area of the electron multipliersurface becomes larger than the even surface so that the secondaryelectron emission efficiency can be improved.

As for a method of coating the grains on the electron multipliersurface, a method whereby they are soaked in solgel liquid, the CVDmethod and so on can be named.

In addition, it is desirable that, by selecting a material of whichsecondary electron emission factor is high as the grain material to becoated, the number of the secondary electrons generated by the electronscolliding with the electron multiplier surface increases. As for suchmaterials of which secondary electron emission efficiency is high withits secondary electron emission coefficient larger than 1 for instance,the oxides such as BeO, MgO and BaO, diamond, graphite, carbon such asglassy carbon or a mixture of them and so on can be named.

Thereafter, as shown in FIG. 4D, the cathode electrode 4 and the anodeelectrode 5 can be formed on both faces of the insulating substrate 1having the channel 2 thus formed so as to render it as a multi-channelplate.

The cathode electrode 4 and the anode electrode 5 are intended to applya potential to the electron multiplier surface 3, and are formed bysputtering or vacuum evaporation of metals such as Au/Ti and Al to beapproximately 0.1 to 0.5 μm thick. On this occasion, evaporation by aparallel beam of metallic atoms is performed so that the metal for theelectrodes will not stick to the inside of the channel 2, and they areformed while having the metallic beam during the evaporation incident ata steep angle on the insulating substrate 1 on which the channel 2 isformed. Or, it is also possible to form it by a printing method not toclose the pores of the channel 2.

According to the present invention, it is possible to form a strong andhomogeneous channel over large area exceeding a micro-size by usingaluminum as the material for forming the insulating substrate so thatthe channel plate of high resolution advantageous for the large area canbe acquired.

In addition, it is possible to form the irregular and minute asperitieson the electron multiplier surface inside the channel so as to acquirethe high secondary electron multiplication factor.

Furthermore, according to the manufacturing method of the presentinvention, the insulating substrate having the channel is formed byregularized aluminum anodic oxidation, and so the channel having theelectron multiplier surface of the high secondary electron emissionefficiency can be easily formed over the large area in a high-resolutionmanner without undergoing a high temperature process.

Moreover, the above-mentioned channel plate may be applied to an X-raydiagnosing apparatus, an X-ray material inspection apparatus and so on.

(Embodiment)

The present invention will be described in detail by taking up anembodiment below.

Embodiment 1

The channel plate of a size of approximately 10 cm was produced.

It will be described hereafter by referring to FIGS. 4A to 4D.

First, the aluminum plate of approximately 12 cm in diameter wasprepared as a material substrate 10 of the insulating substrate 1 (seeFIG. 4A). As for the aluminum plate, one having purity of 99.9 percentor more aluminum was used. First, electrolytic polishing of the surfacewas performed in order to make the aluminum plate surface even. As forthe electrolyte, a mixture of per-chlorous acid (HClO₄) and ethanol(C₂H₅OH) was used to perform it at 100 mA/cm² for three minutes.

Next, the pore 6 was formed on the substrate 10 by the aforementionedtwo-phase anodic oxidation.

An anodic oxidation condition for the first time was 195V, 10 hours inphosphoric acid aqueous solution of 0.3 M of which water temperature waskept at 0° C. Next, etching was performed in the mixture aqueoussolution of chromic acid and phosphoric acid of which water temperaturewas kept at 60° C. for 10 hours or so to remove the anodic oxidationlayer of the first time. Although the anodic oxidation layer was mostlyremoved, regular asperities were left on the aluminum plate surface.

Next, the aluminum substrate thus etched was anodized for the secondtime on the same condition as the first time. Thus, the insulatingsubstrate 1 having regularly formed pores was formed (see FIG. 4B).

The extremely thin oxidation layer was left at the pore bottom 11. Thiszone was removed so as to have the pores extend through the substrateand form the channel 2 as shown in FIG. 4C. The etching was performed bysoaking it in saturated Hg₂Cl₂ solution.

Thereafter, it was soaked in 10 wt % phosphoric acid solution for fourhours and the pore widening process was performed to extend the porediameter.

As a result of observing the insulating substrate formed on thiscondition with an electron microscope, the pores of approximately 250 nmin diameter were formed on the substrate of several hundreds μm inthickness.

The inside of the pore thus formed by the aluminum anodic oxidationformed the uneven surface with irregular and minute asperities.

Thereafter, the inside of the pore was coated with grains. MgO grainswere formed by a solgel method. This formed even more minute asperitiesinside the pore to form the channel 2 having the electron multipliersurface 3 of which secondary electron emission efficiency is high.

Next, the cathode electrode 4 and the anode electrode 5 were formed onboth faces of the insulating substrate 1 having the channel 2. It wasformed by obliquely evaporating aluminum by the vacuum evaporationmethod. Thus, the channel plate was successfully produced (see FIG. 4D).

The channel plate using the nanoholes formed by the anodic oxidation hasvery narrow spacing between the pores so that it is the plate of higherresolution than conventional ones.

What is claimed is:
 1. A channel plate, comprising: a substrate havingplural pores extending therethrough, each pore being defined by arespective inner wall surface of the substrate surrounding the pore; afirst electrode placed on an upper surface of the substrate; a secondelectrode disposed along a lower surface of the substrate; and electronmultipliers comprised of at least one of diamond, graphite, and carbon,or a mixture of at least one thereof, each electron multiplier beingdisposed along a corresponding inner wall surface of the substratesurrounding a corresponding pore.
 2. A photomultiplier having thechannel plate according to claim
 1. 3. The channel plate according toclaim 1, wherein each electron multiplier emits secondary electrons dueto collision of electrons with the electron multiplier.
 4. The channelplate according to claim 1, wherein each electron multiplier has oxidegrains of which a secondary electron emission coefficient is larger thanone.
 5. The channel plate according to claim 1, wherein the substratehas aluminum oxide as a main ingredient.
 6. The channel plate accordingto claim 1, wherein each electron multiplier is formed by coating thecorresponding wall surface of the substrate surrounding thecorresponding pore.
 7. An image intensifier having the channel plateaccording to claim 1.